Indiana Department of Natural Resources sent this bulletin at 08/27/2019 08:19 AM EDT
Weekly Review for Aug. 27, 2019
This informal report by the Division of Entomology and Plant Pathology is designed to update the Nursery and Greenhouse industry of insect and disease pests the Division has been encountering on a week to week basis and as a way to give a “heads up” of things to be on the lookout for. Comments and questions about this report are welcome and can be sent to your respective Inspector.
Not a whole lot of new things out there this past week. Some of the more interesting things I saw were smeared dagger moth caterpillars and cottonwood leaf beetle feeding on hybrid and curly poplar. I also found white marked tussock moth on red twig dogwood. The caterpillars had almost completely defoliated the plants.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
I do not have much to report this week. I have been spending much of my time working on our kudzu suppression program. In my last report a few weeks ago I included images of a leaf spot on tree lilac. Purdue University confirmed the presence of Cercospora and Pseudocercospora were the cause of this angular leaf spot.
This is the first year I have really seen a leaf spot issue on tree lilac. The problem was first found in Bartholomew County, but I am also seeing similar symptoms in Monroe County. In some cases it is cause quite a bit of early defoliation, especially on lower branches. For the second year in a row I have had a severe infection of shot hole fungus on Yoshino cherry in my yard. My tree is once again experiencing early defoliation. The problem is not as serious on my Japanese weeping cherry.
I have seen some leaf spot on river birch, but I have not had significant defoliation this year on my property. Although susceptible to emerald ash borer, the fringe trees on my property look great this year. The foliage is absolutely perfect even after all of the heat and rain. I cannot say the same for my serviceberry. It is about 75% defoliated. I have the straight species of serviceberry. I really recommend planting the cultivar Autumn Brilliance. It seems to be more resistant to leafspot issue and has a much better fall color. One last bid of sad news. My Serbian spruce that has had needle cast infections for 5 years finally died. It took five years to decline. The oriental spruce planted next to it have not shown any symptoms.
Kudzu! I see the stuff in my sleep right now since I am working on the kudzu program. For those of you that are not familiar with kudzu; it is known as the vine that ate the south. Yes it is in Indiana and has even been found in Canada in 2009. Our cold winters really do not kill kudzu. The stuff is amazing and resilient plant. Fifty feet of growth a year is not unrealistic in Indiana and it roots very easily. Suppressing it is very difficult. Eradicating it is probably not likely. During a recent kudzu work I found ambrosia beetle activity on kudzu in Lawrence County. Ambrosia beetles often produce tooth pick like frass spikes on the trunks of infested trees. We have had reports of ambrosia beetles on tulip poplar this year and they can attack almost any deciduous tree.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
I want to show some pictures which to me illustrate the importance of lab testing for many pest and disease issues. The first two pictures are of foliar nematodes on weigela. The symptoms on these leaves are angular purplish black leaf spots, and sometimes the margins are not very defined. On the leaves where the infestation is more advanced, there is an almost mosaic pattern with some yellowing. The next picture is of tree lilac leaves at a different nursery a couple weeks later.
When I sent it to the lab, I suspected foliar nematodes based on what they had looked like in weigela, but this turned out to be either Cercospora or Pseudocercospora. The last two pictures are from an inspection I did last week. The host is another type of tree lilac, and I really wasn’t sure if this was nematodes or fungal again. Especially the last picture to me looked like the more advanced infestation of nematodes, but at the same time many of the leaf spots had diffuse borders similar to the Cercospora/Pseudocercospora sample. This sample also turned out to be Pseudocercospora.
A lot of the pathogens that we encounter in the field can look similar, and it is sometimes difficult to make an accurate diagnosis without a lab test, especially since the same pathogen might manifest differently on different hosts. Even after encountering both of these issues, I can’t say I’d be able to distinguish them in the field on a different host without lab testing.
Lab testing is also important so you know how to properly manage and treat the problem. If you think you have foliar nematodes and use a nematocide but the problem is actually fungal or you use a fungicide when the problem is actually nematodes, your treatment will not be effective.
Inspections over the last week haven’t brought much new but I did see some cool gall on swamp white oak. It’s caused by a cynipid wasp. For the first time this summer, I also saw a lot of Tar Spot on maples. It was mostly on Norway and Sugar maples and had coalesced into larger spots. Unfortunately, also had a find of Hosta Virus X on ‘August Moon’ hostas. Purdue’s Plant & Pest Diagnostic Lab provided the confirmation.
While I am getting to the end of my nursery inspections, I still find things that leave me to marvel at this world we live in. While inspecting a nursery, I heard a lot of buzzing around a couple of ‘Ann’ Magnolias. Closer inspection revealed bald faced hornets – and a lot of them – around the trees. Turns out they were feeding on the sap excreted by the copious amount of scale. I saw Magnolia Scale for sure and there might have been a second, smaller scale, but the hornets dissuaded me from getting a closer look.
Mowing my own yard, I snagged a lilac with the mower handle. Much to my surprise, a large branch broke off at the base of the tree. A closer look showed a lot of damage, probably a combination of lilac borer and the handful of termites I found in the trunk. Curiously, with this much trunk damage, there was little evidence of distress in the canopy of the shrub.
